Impact of crop cultivation, nitrogen and fulvic acid on soil fungal community structure in salt-affected alluvial fluvo-aquic soil

Soil fungal communities play pivotal roles in promoting ecosystem carbon (C) and nitrogen (N) cycling, stimulating disease resistance and enhancing tolerance against salt stress of host plants. However, the impact of anthropogenic management practices on the soil fungal community structure has not yet been clarified. Using a four-consecutive-year field experiment and the quantitative polymerase chain reaction (qPCR) and Illumina MiSeq DNA sequencing methods, the single and interactive impacts of crop cultivation (CK), N fertilization (N) and fulvic acid (F) on soil fungal diversity, abundance, composition and functional groups were investigated. Consecutive crop cultivation improved soil chemical and microbial properties by reducing soil electrical conductivity (ECe) and enhancing soil organic carbon (SOC), microbial biomass carbon (MNC), and microbial biomass nitrogen (MBN). Crop cultivation had larger contribution to fungal richness and diversity than N fertilization and fulvic acid. Crop cultivation enriched mycorrhizal fungi and N fertilization enriched endophytic, saprophytic and pathogenic fungi. Structural equation modeling (SEM) revealed that soil ECe and pH indirectly influenced MBN through their adverse direct impact on OTUs, Shannon index and abundance of predominant fungal taxa. N input exhibited a positive indirect influence on MBN through enhancing abundance of Funneliformis at the genus level. Crop cultivation, N input, and fulvic acid addition in saline soil environment changed the environmental niches and drove the evolution of soil fungal community. In return, the shifts in soil fungal community composition and functional groups greatly affected soil C and N transformation with potential feedback on soil microbial activity.